Salinity impacts both biological and physical components of the ocean ecosystem, including growth rates of marine organisms and vertical stratification Feindel et al. (2013).
Salinity has direct impacts on marine organisms. Different species and life stages have preferred salinity conditions, outside of which they experience deleterious physiological effects, including mortality (Brennan, Blanchard, and Fennel 2016; Feindel et al. 2013). It is expected that many organisms shift their spatial distribution to avoid poor environmental conditions (Nye et al. 2009), although sessile and cultured organisms have limited to no ability to do so. Salinity is of particular concern for shellfish aquaculture. For example, two cultured species in Nova Scotia (blue mussels and oysters) can tolerate a wide range of salinity for short periods of time, but prolonged exposure to low salinity can result in reduced growth and reproduction, higher disease prevalence, and eventually death (Feindel et al. 2013; Howarth, Coughlin, and Reid 2021).
Like temperature, salinity is directly related to seasonal ocean stratification. Freshwater inputs in the spring and summer contribute to a fresh, warm surface layer that disappears in the fall and winter from wind-driven mixing. In turn, salinity is impacted by rates of evaporation and precipitation, freshwater inputs, melting and freezing of sea ice, and ocean circulation (Environment and Canada 2019). Remote sensing observations of salinity, along with temperature and chlorophyll-a, can also be used to estimate ocean acidification (Land et al. 2015; Salisbury et al. 2015).
Surface waters around Canada, including off the coast of Nova Scotia, are generally becoming fresher due to climate change and natural variability (Environment and Canada 2019). This trend is expected to continue as a result of the projected increase in precipitation and ice melt (Environment and Canada 2019; Howarth, Coughlin, and Reid 2021). In contrast, deep waters in the Gulf of St. Lawrence are becoming more saline as a result of the northward shift in subtropical currents bringing in saltier waters (Environment and Canada 2019; Howarth, Coughlin, and Reid 2021).
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